Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $223.47   4.177%   $232.8043   $232.80   $232.80   $232.80  
  Purchase #2 $235.25   13.174%   $266.2418   $266.24   $266.25   $266.20  
  Purchase #3 $78.59   11.554%   $87.6703   $87.67   $87.65   $87.70  
  Purchase #4 $216.56   3.152%   $223.386   $223.39   $223.40   $223.40  
  Purchase #5 $118.55   7.291%   $127.1935   $127.19   $127.20   $127.20  
  Purchase #6 $209.70   3.134%   $216.272   $216.27   $216.25   $216.30  
  Purchase #7 $247.48   5.165%   $260.2623   $260.26   $260.25   $260.30  
  7 purchase totals = $1,329.60       $1,413.8302   $1,413.82   $1,413.80   $1,413.90